I've created an interface in a class model. This interface has two methods, A and B and method A takes an argument (a) and method B does not take an argument (yet).
Additionally I've created a class that implements this interface, overriding both methods.

After a discussing the model method B now should also take a parameter (b), so I modified the interface to reflect this change. However the class realizing this interface is not updated automatically. For one class it's possible to add the method by re-creating the link between the interface, specify the which method should be implemented and deleting this link again. Then the OLD method signature has to be removed as well.
This is a lot of work if there is more then one class implementing the modified interface, not to mention error-prone.

Does anybody know how to make an entire class model update this type of dependency?

In Enterprise Architect, you can automatically override methods from parent Classes and from realized Interfaces.

Select a Class that has a parent or realized interface and select the Element | Advanced | Overrides & Implementations menu option.

In the Override Operations/Interfaces dialog, check the operations/interfaces to automatically override and click on the OK button. Enterprise Architect generates the equivalent function definitions in your child Class.

You can configure Enterprise Architect to display this dialog each time you add a Generalization or Realization connector between Classes, and review their possible operations/interfaces to override/implement. Do this from the Links page of the Options dialog (select the Tools | Options | Links menu option).

This does not cover adding or removing parameters from a method. Nor does it cover removing a method from the interface. Additionally this is still manual work which I am simply to lazy to do.
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TimoFeb 15 '13 at 11:07